Marketing is not my expertise, but if you're after making money from domains, here's my advise:
First you need to know your budget, let's say you have a $1,000.
Next you need to know your target, let's say 4L .com.
Now bearing in mind that market is down, you can really get a lot of domain for your $1,000. Here's how:
DO NOT go ahead and be like 90% people here & grab a $100 4L .com thinking that buying 10 domains is a bargain. Let's say you are planning to keep them for 2 years to sell them when the market is better, this is 10 names x 10 renewal fees x 2 years = $200. avoid this senior.
back to your 1,000 budget. buy a premium domain for 700-900. save 100-200
Sell this name for 1,500 (which should be easy if the name is great!). now you have 1,500 + what you saved. Next, buy a 1,300 domain & sell it for 2k.
Repeat this, and in 1 year you'll reach 100k before you know it. Having top domains people will reach you & less marketing will be needed.
Again, that's only my opinion, by time you will grow your own techniques. buying the cheapest investments is not always advisable, unless you really know what you're doing.
Hope this helps,
Amr